Is there a MacBook USB C Adapter that allows me to charge and connect an external hard drive at the same time?

Yes, Apple sells one, but I don't recommend it. The Apple USB-C Digital AV Multiport Adapter should do it, but it wouldn't recognize USB3 external drives for me. And, I tried two of them.

Buy one from these guys: https://www.hypershop.com/collections/hyperdrive They actually work and cost $20 less.

I suppose Apple USB-C Digital AV multi port adapter can connect external HDD and charging battery at the same time, though I'm not sure your external HDD is bus powered or self powered, since it provides only 55W.

I think you should contact Apple and ask about it.